This invention relates to plasticizers for vinyl chloride polymer films and plastisols used in production of such films. In particular, the invention relates to plasticizers with which such plastisols and films can be made using relatively small amounts of plasticizing ester, and to the production of highly stain-resistant vinyl chloride polymer films. Efforts to develop such films are especially important in the vinyl floor covering industry due to the much greater consumer appeal of flooring resistant to common stainants including shoe polish, mustard, road surfacing materials such as asphalt, etc.
In general, it is very desirable to produce plasticized vinyl chloride polymer films without the costs of intensive mixing of polymer and plasticizer, e.g. in a Banbury mixer. Thus for economic reasons, the expedient of plastisol application of vinyl chloride polymer films is employed whenever feasible. In accordance with that technique, now well known in the art, finely divided vinyl chloride polymer (hereinafter "VCP") is essentially uniformly dispersed in an amount of plasticizer sufficient to form a plastisol (normally at ambient temperature) of viscosity low enough for reasonably rapid escape of entrained air and for convenient casting of the plastisol on a solid surface where it will be fused to form an essentially homogeneous, molten film and then cooled to solidify that film. In addition, the amount of plasticizer employed must be sufficient to provide satisfactory plasticization of the film as shown by its flexibility, percent elongation at break, etc.
In general, plasticizers used in preparation of such plastisols are advantageously carboxylic acid esters such as alkyl benzyl phthalates, dialkyl phthalates, alkyl benzoates, etc. Various diluents, e.g. hydrocarbons which flash off during plastisol processing, may help maintain a desirably low plastisol viscosity but not substantially enhance the plasticizing of the resulting film. In addition, use of an excess of such diluents may contribute to other problems such as "blooming" from the film of soaps present in VCP from its production by emulsion polymerization. Thus a certain amount of "prime" ester (i.e., ester which remains in the VCP film or other composition after fusing and solidification of the VCP plastisol) is normally considered necessary in plastisol application of VCP, and it is usually expected that the required amount of such prime ester will be from 35 to 70 or more parts per hundred parts by weight of the VCP. See, for example, "Vinyl Dispersion Coatings for Foam Floorings and Fabrics", L. G. Friedman, Soc. of Plastics Engineers, 28th Annual Technical Conference, pp. 226-31 (1971) and Vol. 3, Encyclopedia of PVC, Marcell Dekker, Inc., New York and Basel, p. 1426 (1977).
Unfortunately, the staining tendency of the resulting VCP film is typically more or less proportional to the amount of plasticizing ester present in the film and consequently, it is highly desirable to identify an ester-containing plasticizer composition which can be used to provide an attractively low plastisol viscosity and good plasticization of the resulting film when used in amounts small enough to interfere relatively little with the natural stain resistance of the VCP. Thus it is an object of this invention to provide a more efficient plasticizer composition such that plastisol-applied films produced therewith are more highly stain-resistant. Other objects are VCP compositions containing such a plasticizer composition and, in particular, a relatively small but adequately plasticizing amount of such a plasticizer composition. Another object is to provide VCP plastisol compositions which can be cast in a film on a solid surface, fused and then cooled to provide a solid, plasticized film (e.g. a floor covering wear layer) having a high degree of stain resistance. Other objects include the resulting stain-resistant floor covering wear layers and other solid films. Another object is the provision of a method for producing such VCP plastisols and the stain-resistant floor covering wear layers and other solid films made from such plastisols. Other objects will be apparent from the following disclosure in which all parts and percentages are by weight except where otherwise noted and "phr" represents parts per hundred parts by weight of VCP in any given composition.